1. Field of the Invention
The invention relates to semi-trailer air-ride axle/suspension systems, and in particular to the automatic pneumatic control system for the air springs of its suspension assemblies. More particularly, the invention is directed to an automatic pneumatic control system for suspension air springs which includes a pilot valve that is sensitive to differing air pressures in certain parts of the system, resulting in rapid, generally instantaneous exhaustion of a sufficient amount of air from the springs when the vehicle is docked and before the parking brakes are set or engaged, thereby minimizing or eliminating the problems of sudden trailer drop and trailer walk or movement away from the dock during loading of the trailer.
2. Background Art
Many commercial semi-trailers utilize air-ride axle/suspension systems to provide a smooth ride for cargo carried by the vehicle, as well as to ensure a comfortable ride for the operator and any passengers riding in the semi-trailer cab or tractor. A key component of an air-ride axle/suspension system is its air springs. However, such air springs, while providing a softer ride during operation of the vehicle, are not conducive to stability during loading of the trailer. More specifically, before loading of the trailer is to commence at a dock, the suspension air springs typically are exhausted of a sufficient amount of pressurized air to enable the frame of the trailer to be lowered until it contacts physical stops or bumpers conventionally located within the air springs. This lowering of the frame against the bumpers makes the trailer more stable for a loading operation. A pilot valve, typically referred to in the industry as an automatic or gladhand dump valve, is connected to the pressurized air supply of the semi-trailer and each air spring, and controls inflation and deflation of its respective air spring.
However, conventional automatic suspension air spring control systems currently in use in the semi-trailer industry, while achieving their intended result, fail to achieve optimum stability of the semi-trailer during loading operations. More particularly, the pilot valves of these prior art control systems operate only in response to the pressure status of the air conduits that are directly connected to the vehicle parking brake. Such control systems necessarily are tied-in to the status of the parking brake for obvious safety reasons. Specifically, it would be undesirable for the air springs to exhaust when the parking brake is disengaged and the semi-trailer is operating over-the-road. Thus, when the parking brakes are released or disengaged for over-the-road travel, the parking brake air conduits are sufficiently pressurized to overcome the spring bias that engages the brake, thereby maintaining the brake in a released condition. A pressure sensor line transmits this higher air pressure to the pilot valve, and the pressure in the sensor line also is sufficiently high to overcome the pilot valve spring bias to the closed position and shift it to the open position to cause inflation of the air spring through the opened valve to a selected over-the-road operation ride height. Because such pilot valves typically activate or open automatically when the parking brakes are released, no driver interaction or training is required. Conversely, when the parking brakes are engaged, such as when the semi-trailer is docked for loading, the valve automatically closes, air pressure is exhausted from the air springs, and the vehicle frame lowers into contact with the air spring bumpers. This contact of the frame with the bumpers creates a more stable condition for trailer loading.
However, the above-described prior art control system may not always be completely effective for its intended purpose when the docked trailer is empty and the axle/suspension system has a trailing beam design. Specifically, a trailing beam pivots at its bushing mounting to the vehicle frame hanger. This pivotal attachment structure at the front end of the beam is what allows the trailer frame,to lower when air is exhausted from the air spring located at the opposite or rear end of the beam. However, the air spring control systems commonly in use today do not begin exhausting air pressure from the springs until the parking brakes already are begining to engage or are engaged and such engagement typically occurs very quickly, taking only about 1.5 seconds. Thus, in order for the trailer frame to lower once the parking brakes are set, which is before a sufficient amount of air contained in the air springs is exhausted, the tires must rotate together with the pivoting suspension beam or the engaged parking brakes must drag against their engagement force. However, an empty trailer fails to generate enough force to overcome the brake engagement forces or the friction forces between the tires and the ground. Thus, in such a situation, the trailer frame is maintained at ride-height, even though the trailer is docked and air has been exhausted from the air springs. Despite being strong enough to maintain the trailer frame at its operational height after exhaustion of air from the air springs of an empty trailer, such tire-ground friction forces and parking brake engagement forces nonetheless are relatively weak. Therefore, when a towmotor or forklift is driven onto the trailer deck from the dock to begin loading the trailer, such tire friction or brake engagement forces typically are overcome by the weight of the towmotor and its driver. As a result, the trailer frame drops suddenly against the bumpers of the previously deflated air springs. In addition, the arcuate movement of the trailing beam and possible resulting forward rotation of the tires also can cause the trailer to move or xe2x80x9cwalkxe2x80x9d away from the dock. Such a sudden drop and forward movement of the Trailer deck, while unnerving to the towmotor operator, also can cause damage to the trailer landing gear and disengagement of the loading ramp dock plate. These conditions are undesirable. The present invention reduces or eliminates the incidence of trailer drop and walk by exhausting a sufficient amount of air from the air springs, and bringing the trailer frame in contact or nearly in contact with the air spring bumpers before engagement of the parking brake.
Objectives of the present invention include providing an automatic pneumatic control system for suspension air springs capable of exhausting a sufficient amount of air from the springs generally instantaneously and before engagement of the parking brakes, thereby enabling the trailer frame to lower against the air spring bumpers.
Another objective of the present invention is to provide such a pneumatic control system which is economical, durable and reliable in use, and easy to install, maintain, and use.
These objectives and advantages are obtained by the pneumatic control system for the air springs of a vehicle axle/suspension system of the present invention, wherein the control system includes a plurality of conduits and valves extending between and pneumatically interconnecting at least one source of pressurized air, at least one vehicle parking brake and the air springs, and pilot valve means for controlling the inflation and deflation of the air springs, the valve means closing in response to differing air pressures in the control system resulting from initiation of engagement of the parking brake, so that a sufficient amount of pressurized air is exhausted from the air springs through the valve means to substantially deflate the air springs before the parking brake is engaged.